The present invention relates generally to printers, and more particularly to a printer assembly and to a method for determining the position of a printer component.
Printers include those printers having a printer component, such as a printer paper-feed roller, whose position must be determined for accurate operation of the printer. Typically, an analog encoder is operatively connected to the printer paper-feed roller, and an analog-to-digital converter is operatively connected to the output of the analog encoder to sample the analog encoder signals. The position of the paper-feed roller is determined from the output of the analog-to-digital converter. However, an expensive analog-to-digital converter must be used to sample the incoming signals fast enough (i.e., accurate enough) that no position information is lost.
What is needed is an improved printer assembly and an improved method for determining the position of a printer component such as a printer paper-feed roller.
A first embodiment of the invention is for a printer assembly having a printer component, a processor, an analog encoder, and a threshold device. The printer component is movable from an initial position toward a desired final position. The threshold device has a digital output connected to the processor. The analog encoder is operatively connected to the printer component and has an analog output connected to the threshold device and operatively connected to the processor. The processor determines the position of the printer component from the digital output and a digitization of the analog output.
A first method of the invention is for determining the position of a printer paper-feed roller during a paper index move from an initial position toward a desired final position, wherein an analog encoder is operatively connected to the printer paper-feed roller, and wherein a threshold device is connected to the analog output of the analog encoder. The first method includes steps a) through f). Step a) includes selecting a digital coarse position transition point. Step b) includes selecting an analog fine position transition point. Step c) includes initially determining the position as a digital coarse position from the digital output of the threshold device. Step d) includes determining a digitized fine position from the analog output of the analog encoder starting when the determined digital coarse position first is at least equal to the digital coarse position transition point. Step e) includes setting a digitized analog coarse position equal to the digital coarse position when the determined digitized analog fine position first is at least equal to the analog fine position transition point. Step f) includes, after step e), calculating the position by combining the set digitized analog coarse position and the determined digitized analog fine position. In one implementation of the first method, the threshold device is a Schmitt-trigger threshold device. In the same or another implementation of the first method of the invention, the analog output includes periodic first and second analog signals substantially ninety degrees out of phase, and the digital output includes a first digital signal corresponding to the first analog signal and a second digital signal corresponding to the second analog signal.
A broadly described expression of a method of the invention is a method for determining the position of a printer component during a move of the printer component from an initial position toward a desired final position, wherein an analog encoder is operatively connected to the printer component, and wherein a threshold device is connected to the analog output of the analog encoder. The broadly described expression of the method of the invention includes steps a) through f) which are identical to steps a) through f) described above for the first method of the invention.
Several benefits and advantages are derived from the first embodiment of the invention and from the first and the broadly-described expression of a method of the invention. Accurate digital coarse position information is obtained from the threshold device. Accurate digitized analog fine position information is obtained from the analog encoder through a low-cost analog-to-digital converter (ADC). Synchronization of the digital coarse position to the digitized analog coarse position is done by selecting a digital coarse position transition point and an analog fine position transition point which enables the digitized analog fine position to be associated with the correct digital coarse position despite uncertainties in switching of the threshold device. The expensive high-sampling-rate ADC of the prior art is replaced with the previously-described low-cost ADC and with an inexpensive threshold device, such as a Schmitt-trigger threshold device. The low-cost ADC results from choosing a digital coarse position transition point corresponding to when the position of the printer paper-feed roller or other printer component is changing slowly enough (usually near the end of a move) so that a low-sampling-rate ADC provides the desired sampling rate.